1. Field of the Invention
The present invention generally relates to a method of reducing power consumption in a disk drive system, and more particularly, to a read/write head actuator that is controlled so as to reduce power consumption without sacrificing data access time.
2. Description of the Related Art
Reducing power consumption is a basic requirement for disk drive data storage systems. In particular, users of mobile and notebook computer systems view battery life between charges as one of the most important system characteristics. As such, methods of reducing power consumption, or battery power management, are crucial to extending the life of the battery between charges.
One such power management design is based on the fact that in a typical disk drive data system operation, the disk drive is not always conducting reading and writing operations. Thus, there are certain periods of non-work or low power consumption. Firmware or software can be designed to control the flow of battery power based on this model. Using such a power management system, the typical disk drive power specifications for an IBM Travelerstar 4LP, for example, are listed in Table 1 below, with a typical dissipation of 0.94 amps:
TABLE 1 ______________________________________ Power Consumption For Each Disk Drive Mode Disk Drive Mode Power ______________________________________ Start-Up (Maximum Peak) 2.3 Watts Seeking (Average) 2.3 Watts Read/Write (Average) 1.85 Watts Performance Idle (Average) 0.85 Watts Low Power Idle (Average) 0.3 Watts Sleep 0.1 Watts ______________________________________
In the start-up mode, the power consumption is mainly due to the operation of the spindle motor, which rotates a disk platter.
The track and sector seeking and read/write modes identify the power consumption during normal operations. In such normal operations, an actuator supports one or more read/write heads, with the actuator being driven by an actuator motor (also called a voice control motor (VCM)). Current is passed through an actuator coil, causing the actuator motor to rotate the actuator and read/write heads to radial data tracks on the disk platter surface. As shown in Table 1, the more reading and writing operations that are conducted, the more seeking operations that must be carried out, and consequently, the more power will be consumed. Also note that the seeking operations require the most power.
The performance idle, low power idle and sleep modes represent the power consumption resulting from a power management scheme. In this example, power consumption is reduced by about 31% over the conventional disk drive system without power management. Such an exemplary power management technique is shown in, for example, U.S. Pat. Nos. 5,452,277, 5,544,138 and 5,521,896. Such patents compare energy usage with a predetermined profile to select one of several reduced power operating modes.
Other methods of power consumption control the rotation of the spindle motor, and thus the disk platter, to reduce power consumption as shown in U.S. Pat. Nos. 5,345,347 and 5,493,670.
In U.S. Pat. No. 5,140,571, power consumption is reduced using a digital signal processor (DSP) during intermittent periods. However, the amount of power consumed by the DSP is relatively low compared with the power used for driving the actuator motor and spindle motor.
In U.S. Pat. No. 5,412,809, a user can select either a performance optimized control assess time algorithm, or a power consumption optimized control assess time algorithm. This method, however, supplies just these two options. Another disadvantage is that the reduced power consumption option sacrifices the average access time to achieve its goal.
While each of the above power management methods reduces overall disk drive power consumption somewhat, none reduce the main component of the disk drive's power consumption, namely, the seeking procedure, without sacrificing data access time.
In all the above power management methods, the seeking procedures are implemented under the assumption that the actuator is controlled to move the read/write heads as fast as possible from one track to another track in a "track seeking" mode. Once the heads land on the designated track, the servo system typically enters a "track following" mode to find a desired sector within the track. The "track following" mode consumes much less power than the "track seeking" mode. This is because the maximum current is supplied to the power amplifier and actuator coil in the track seeking mode to move the head as fast as possible. The more current supplied to the actuator coil, the faster the actuator arm is rotated and the faster the heads move.
In light of the foregoing, there exists a need for a method of reducing the power consumption associated with the seeking operation, without sacrificing data access time.